Lidar

ABSTRACT

A lidar, which includes a transmitter and a receiver, as well as an optical system, which is arranged to direct at least part of the light sent by the transmitter as a transmitter beam progressing towards an object and to define the receiver beam to the receiver, at least part of the light arriving from the zone of which is focussed on the receiver. The optical system of the lidar is implemented in such a way that the beams immediately in front of the lidar are located essentially outside of each and one of the beams at least partially surrounds the other beam. The optical system includes an integrated optical, which has a first area for forming the transmitter beam, and a second area for forming the receiver beam.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims priority under 35 U.S.C. §119 to PCTPatent Application No. PCT/FI03/00143, filed Feb. 28, 2003, and FinnishPatent Application No. 20020394, filed Feb. 28, 2002, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a lidar.

2. Description of Background Art

A lidar of this kind is used to perform measurements, in such a way thata transmitter beam is sent towards the object to be measured and thereturning signal coming back from the direction of the object beingmeasured is observed. The return signal is formed when the light of thetransmitter beam is scattered and/or reflected by the object beingmeasured.

The lidars to which the present invention relates are particularly usedfor making meteorological measurements. The commonest measurementsperformed with the aid of the lidar are cloud ceiling measurements,visibility measurements, and determining the structure and height ofatmospheric boundary layers.

FIG. 1 shows the optical construction of one lidar according to theprior art.

FIG. 2 shows the optical construction of a second lidar according to theprior art.

The lidar of FIG. 1 includes a transmitter 1, typically a pulsed laserdevice, which produces the light to be transmitted, and a receiver 2, bymeans of which light can be received at the transmitted wavelength. Thelidar also includes a lens 13, which aligns the light transmitted by thetransmitter 1 to form an essentially parallel transmitter beam 14. Thefigure also shows particles 15 in the atmosphere, from which thetransmitter beam 14 is scattered and/or reflected. Part of the scatteredand/or reflected light 16 proceeds to the lens 13, which focuses thelight on its focal point. In addition to the object, the light is alsoscattered by the surfaces, particles, and air molecules inside the lidarand in its vicinity. In terms of the measurement of the object, thisextremely powerful signal component is a disturbance, which can becalled crosstalk. The light scattered from the atmosphere at a closemeasurement distance from the lidar is, like the crosstalk significantlystronger that the signal received from a great distance, becausescattered light attenuates in proportion to the square of the distance.In addition, multi-scattered light arrives at the receiver 2, both fromthe object and from the atmosphere between the lidar and the object.Here, the term multi-scattered light refers to re-scattered light, i.e.light that has been scattered through more than one particle.

In the lidar of FIG. 1, the receiver 2 cannot be located at the focalpoint of the lens 13, because the transmitter 1 is at the focal point ofthe lens. The lidar is therefore equipped with a beam splitter 17, whichreflects the light coming from the lens 13 to the receiver 2. Thus, areflected focal point is created for the receiver 2, the lens 13focussing onto it the light arriving at the lens 13 from the directionof the central axis of the lens. Thus, a field of vision, whichcorresponds with a good degree of accuracy to the shape of thetransmitter beam 14, is created for the receiver 2. The field of visionof the receiver is also called the receiver beam. In the solution shownin FIG. 1, the central axes of the transmitter beam 14 and of the fieldof vision lie on the same line, allowing it to be termed coaxial lidar.

In the coaxial solution according to FIG. 1, a problem arises in theform of crosstalk and excessive scattering in the near zone of thelidar, or at close measurement distances. Excessive near-zone scatteringcan upset measurement in the lidar's entire measurement range, becausethe receiver 2 can then become saturated by the excessively strongbackward signal.

Here, the term near zone refers to the area extending from inside thelidar to the start of the desired measurement range (e.g., 0.1 m). Themeasurement range, on the other hand, is the distance that starts fromthe near zone and terminates at the maximum measurement range. In thiscase, the measurement range is divided into near measurement distancesand the rest of the measurement range.

Lidar solutions are also known, in which the effect of near-zonescattering is less, because the transmitter beam and the field of visionof the receiver are located separately from each other. Such a solutioncan be termed biaxial lidar. In biaxial lidar, a one time scatteredsignal component is not received from the near zone; instead the signalreceived from the near zone is mainly multi-scattered light. Biaxiallidar is implemented by using two separate optical systems, one of whichforms the transmitter beam and the other focuses the returning light onthe receiver. In such a solution, there is considerably less scatteringof the light into the receiver, when compared to the solution of FIG. 1.However, the solution is more complex and expensive, as it requiresseparate optical systems, typically lenses and systems of lenses, forboth the receiver and the transmitter. Because the optical systems ofthe receiver and transmitter are separate from each other, the internalfocussing of the apparatus is also difficult. If the central axis of thetransmitter beam is not aligned with the central axis of the receiverbeam, the transmitter beam can diverge from the receiver beam, in whichcase the signal returning from the near measurement distances willmainly comprise multi-scattered light, making the measurement moreuncertain. The focussing error can also change during operation, due tomutual movement between the optical systems or vibration, so thatmeasurement becomes unstable. In addition, in principle an error canarise from the fact that the scattering or reflection of the object andthe medium do not behave symmetrically in relation to the transmitterbeam. All in all, biaxial lidar is less stable than coaxial lidar ofcorresponding quality.

In addition, a lidar solution is known that utilizes a Cassegraintelescope, and in which the outgoing beam is reflected by means of amirror located above the Cassegrain telescope. FIG. 2 shows a schematicdiagram of such a solution. The lidar shown in FIG. 2 includes, like thelidar of FIG. 1, both a transmitter 1 and a receiver 2. Light isreceived by means of the Cassegrain telescope, which includes mirrors 23and 24 that collect the light arriving from the area of the field ofvision and focus it through a hole in the mirror 23 to the receiver 2.The lidar also includes a mirror 25, which is located above the mirror24, in such a way that the outgoing light can be reflected to form atransmitter beam, which is located at least in the near zone of thelidar, in the centre of the field of vision of the receiver. In asolution like that of FIG. 2, some of the advantages of a biaxialsolution and the coaxial solution depicted by FIG. 1 can be combined.This is because, in the solution of FIG. 2, the transmitter beam and thefield of vision of the receiver do not overlap so much in the near zoneof the lidar. In addition, the small alignment error of the transmitterbeam and the field of vision of the receiver is compensated at leastpartially by the fact that the field of vision of the receiver islocated around the transmitter beam. A drawback with the Cassegrainsolution is its complexity. To operate satisfactorily, the Cassegrainsolution also requires the mutual alignment of several opticalcomponents. In the solution of FIG. 2, the following precise alignmentsat least must be made:

-   -   centering and orientation of the mirrors 23 and 24 of the        telescope    -   centering of the receiver 2    -   focussing of the receiver (generally carried out by adjusting        the distance between the mirrors 23 and 24)    -   focussing of the transmitter 1    -   parallel alignment (with the aid of the mirror 25) of the        transmitter beam and the receiver beam (field of vision of the        receiver).

This means that making the solution according to FIG. 2 ready to operateis quite demanding. Perhaps the most demanding of the aforementionedalignment stages is making the transmitter beam and the receiver beamparallel to each other. The parallel alignment of the beams can beparticularly difficult, if it must be carried out in field conditionsafter the lidar has been moved.

Thus, each of the known solutions referred to above has its owndrawbacks, which reduce its attractiveness and usefulness. A coaxialsolution like that shown in FIG. 1 has the problem of excessivenear-zone scattering. A biaxial solution has, in turn, the problem ofaligning the transmitter beam and the receiver beam and the very greatinfluence of an alignment error on the strength of the received signal.In the solution according to FIG. 2, though an alignment error betweenthe transmitter beam and the receiver beam has less effect than in thebiaxial solution, the actual alignment is even more difficult that inthe biaxial solution. In other ways too, the device shown in FIG. 2 iscomplex and demands more alignment operations that the other solutions.

SUMMARY AND OBJECTS OF THE INVENTION

Object of the invention is to create an improved optical structure forlidar, in which it would be possible to combine more than previously ofthe beneficial aspects of the aforementioned prior art, whilesimultaneously avoiding at least some of the problems associated withthe prior art. An object of the invention is particularly to create anoptical structure, which, in terms of its structural properties wouldpermit

-   -   greater stability compared to the known biaxial structure,    -   less near-zone scattering than the known coaxial lidar (the        solution of FIG. 1), and    -   nevertheless be easier to align than the known Cassegrain        solution (FIG. 2).

The invention is based on refracting the transmitter beam and thereceiver beam within a single optical system, principally with the aidof a single integrated optical component. The edge area of theintegrated optical component is used to refract one of the beams whilethe central area of the integrated optical component is used to refractthe other beam. In this case, the term refracting refers to focussing ona common focal point light rays proceeding parallel to each other, orfocussing light rays diverging from a common focal point to form lightrays that proceed in parallel. The refraction can thus be carried outwith the aid of, for example, a lens or a curved mirror. The termintegrated optical component, in turn, refers to an optical component,which participates in refracting both the transmitter beam and thereceiver beam, and which can be mechanically handled as a single piece.The integrated optical component can be formed of a single opticalelement, such as a lens or a mirror. Thus, a single lens can act as theintegrated optical component referred to here. Alternatively, theintegrated optical component can be formed of more than one opticalelement, by connecting them together in such a way that they operatemechanically as a single piece. Besides the integrated opticalcomponent, at least one reflection is designed for the optical system,so that the focal point of the light refracted in the edge area of theintegrated optical component lies at a distance to the focal point ofthe light refracted in the centre area of the integrated opticalcomponent. Thus, the transmitter beam and the receiver beam are formedto lie inside each other, so that, in the near zone of the lidar, thefield of vision of the receiver surrounds the transmitter beam, or thetransmitter beam surrounds the field of vision of the receiver. However,the solution, in which the field of vision of the receiver lies aroundthe transmitter beam, is regarded as the better of these twoalternatives.

Considerable advantages are gained with the aid of the invention.

This is because a solution according to the invention can be implementedin such a way that:

-   -   The transmitter beam and the receiver beam surround, but do not,        at least to any great extent, intersect each other in the near        zone, so that the strength of the signal coming from the near        zone is clearly less (multi-scattering in the air always creates        a certain signal component) than in the known coaxial solution.    -   The transmitter beam and the receiver beam surround, but do not        intersect each other in the near zone, so that, unlike the known        biaxial solution, the structure permits a clearly more stable        received signal with a specific precision of adjustment.    -   The principal refraction of the transmitter beam and the        receiver beam is carried out using an integrated optical        component, which operates mechanically as a single piece, so        that the lidar has a relatively simple construction and is        clearly easier to align than in the known Cassegrain solution.

In the solution according to the invention, the alignment of the lightcan thus take place with the aid of a single optical system whilenevertheless be arranged so that the field of vision of the receiver andthe transmitter beam do not coincide in the near zone of the lidar. Thispermits greater stability than with the known biaxial structure, andsimultaneously less near-zone scattering than in the known coaxiallidar.

The invention has also several embodiments, by means of whichsignificant additional advantages are obtained.

In one embodiment of the invention, the transmitter beam and the fieldof vision of the receiver are located in the optical system at adistance to each other, in such a way that a so-called ‘dark’ zoneremains in the near zone of the lidar, between the transmitter beam andthe field of vision of the receiver. The ‘dark’ zone is thus locatedannularly around the transmitter beam while the field of vision of thereceiver is located around the ‘dark’ zone. In the embodiment in whichthe transmitter beam surrounds the field of vision, the ‘dark’ zone islocated correspondingly around the receiver beam. The ‘dark’ zone isthus a zone, which the transmitter beam does not strike and which alsois not included in the field of vision of the receiver. Theimplementation of the ‘dark’ zone between the field of vision and thetransmitter beam further significantly reduces the scattering from thetransmitter beam to the receiver, in the near zone of the lidar. As thedistance increases, the transmitter beam and the field of visiondiverge, i.e. expand, so that despite the ‘dark’ zone, the field ofvision and the transmitter beam begin to partly overlap each otherwithin the measurement zone of the lidar.

A second embodiment of the invention has the additional advantage thatthe lidar can be made more efficient than the known solution shown inFIG. 1, as, in the preferred embodiment of the invention, the losscaused by the semi-translucent mirror is saved. In turn, the improvementin efficiency permits the receiving surface area and thus the entireoptical system to be given smaller dimensions. At the same time, thefocal length can be reduced, which also helps to make the apparatussmaller.

In a third embodiment of the invention, the shapes of the transmitterbeam and the field of vision are essentially rotationally symmetricalaround their common central axis. This achieves the additional advantagethat the symmetry of the system at least partly compensates for theobject's possibly asymmetrical reflecting or scattering behaviour.

In the following, the invention is examined with the aid of examples andwith reference to the accompanying drawings.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description given hereinbelow and the accompanying drawingswhich are given by way of illustration only, and thus are not limitativeof the present invention, and wherein:

FIG. 1 shows the optical construction of one lidar according to theprior art.

FIG. 2 shows the optical construction of a second lidar according to theprior art.

FIG. 3 shows a schematic diagram of one solution according to theinvention.

FIG. 4 shows a schematic diagram of a second solution according to theinvention.

FIG. 5 shows a schematic diagram of a third solution according to theinvention.

FIG. 6 shows a schematic diagram of a fourth solution according to theinvention.

FIG. 7 shows a schematic diagram of a fifth solution according to theinvention.

FIG. 8 shows a schematic diagram of a sixth solution according to theinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The solution of FIG. 3 includes an integrated optical component 6 and areflecting element 7, with the aid of which a transmitter beam 3 and areceiver beam 4 are formed. The integrated optical component 6 consistsof, in this solution, a single lens 33. A mirror 34, in the centre ofwhich a hole has been made, acts in turn as the reflecting element 7.The mirror 34 is positioned in such a way that the light obtained fromthe transmitter 1, which is located at the focal point of the lens 33,is directed through the hole in the mirror 34 to the central area of thelens 33, where it is refracted to form a transmitter beam of the desiredshape. The mirror 34, however, is positioned so that the light arrivingfrom the area of the desired receiver beam to the edge area of the lens33 is refracted and reflected towards the reflected focal point. Thereceiver 2 is located at this reflected focal point.

In the basic solution of the embodiment of FIG. 3, there are thus fouroptical components to be positioned in relation to each other, i.e. theintegrated optical component formed by the lens 33, and the transmitter1, the receiver 2, and the mirror 34. Of these components, the lens 33and the mirror 34 perform the principal refraction of the light and itsdivision between two focal points. The other components shown in thefigure are optional accessories, which, in some embodiments, can beused, for example, for dimensioning purposes, or to alter the shape ofthe beam of the receiver 2 or the transmitter 1 to conform to theoptical properties of the lidar. These optional accessories are thepre-optics of the transmitter 1 and the pre-optics of the receiver 2.The pre-optics of the transmitter 1 can include one or more lenses 35and/or a beam restrictor 36. The lens or lenses 35 are used, ifnecessary, to focus or shape the beam of the transmitter 1. The beamrestrictor 36, which can be, for example, a plate with a hole, is usedin turn if necessary to restrict the beam of the transmitter 1 to form asuitable shape. Correspondingly, the pre-optics of the receiver 2 caninclude one or more lenses 37 and/or a beam restrictor 38. Thepre-optics are thus intended to adapt the receiver 2 or the transmitter1 to the actual optical structure 6, 7 of the lidar. Refraction that mayoccur in the pre-optics is not therefore regarded as part of therefraction taking place in the optical structure 6, 7 of the lidar.

In the solution of FIG. 3, the receiver beam 4 has an annular shape andsurrounds the transmitter beam 3. In addition, a ‘dark’ zone 5 isdesigned between the beams, to reduce the reception signal caused byreflection and simple scattering in the near zone. Thus, the signalreceived from the near zone is mainly caused by multi-scattering.

The solution of FIG. 4 includes an integrated optical component 6 and areflecting element 7, with the aid of which a transmitter beam 3 and areceiver beam 4 are formed. In this solution, the integrated opticalcomponent 6 consists of a single lens 43. A mirror 44, which is alignedmore or less with the central area of the lens 43, acts as thereflecting element 7. The mirror 44 is positioned in relation to thetransmitter 1 in such a way that the mirror 44 reflects the focal pointof the central area of the lens 43 to the transmitter 1. Thus, the lightobtained from the transmitter 1 can be reflected through the mirror 44to the lens 43 and refracted in the central area of the lens 43 to forma transmitter beam 3 of the desired shape. The mirror 44, however, ispositioned so that it does not obscure the desired field of vision ofthe receiver 2, but preferably even restricts the receiver beam to thedesired shape, by obscuring the central area in front of the receiver 2.The receiver 2 is thus located at the focal point formed from the edgearea of the lens 43.

In the basic solution of the embodiment of FIG. 4, there are fouroptical components positioned in relation to each other in the same wayas in the solution of FIG. 3, i.e. the integrated optical componentformed by the lens 43, and the transmitter 1, the receiver 2, and themirror 44.

In the solution of FIG. 4, optional accessories can be used in the sameway as in the solution of FIG. 3. Possible accessories include thepre-optics of the transmitter 1 or the receiver 2, which can include oneor more lenses and/or a beam restrictor. As in the solution of FIG. 3, a‘dark’ zone is designed in the solution of FIG. 4, between the receiverbeam 4 and the transmitter beam 3.

The solution of FIG. 5 includes an integrated optical component 6 and areflecting element 7, with the aid of which a transmitter beam 3 and areceiver beam 4 are formed. In this embodiment, even the reflectingelement 7 is integrated to form a single mechanical unit with theintegrated optical component 6. In this solution, the integrated opticalcomponent 6 is formed of two curved mirrors 53 and 54 joined together.The outer curved mirror 53 reflects to a focal point outside the beams 3and 4, where the receiver 2 is located and to which the receiver beam 4is focussed from the surface of the outer curved mirror 53. The innercurved mirror 54 also reflects to a focal point outside the beams 3 and4, but the inner curved mirror 54 is rotated in relation to the outercurved mirror 53 in such a way that the focal points reflected by themirrors 53 and 54 lie at a suitable distance to each other. Thetransmitter 1 is located at the focal point reflected by the innercurved mirror 54, so that the light obtained from the transmitter isrefracted in the central area of the curved mirror 54 into a transmitterbeam 3 of the desired shape.

In the embodiment of FIG. 5, a particularly interesting feature is thatit does not require a separate reflecting element 7, as both of therefracting members 53 and 54 contained in the integrated opticalcomponent 6 are themselves reflecting. Thus, the reflecting element 7too is integrated as a single mechanical piece with the integratedoptical component 6. This has the significant effect, in a lidaraccording to such an embodiment, of also not requiring the separatefocussing of the reflecting element 7 and the integrated opticalcomponent 6, which are instead focussed at the same time and are alwaysmutually correctly positioned. Thus, in the basic solution of theembodiment of FIG. 5, only three optical components must be positionedrelative to each other, i.e. the integrated optical component (whichalso acts as the reflecting element 7) formed of the mirrors 53 and 54,the transmitter 1, and the receiver 2.

In the solution of FIG. 5, optional accessories can be used, as in thesolution of FIG. 3. Possible accessories include the pre-optics of thetransmitter 1 or the receiver 2, which can include one or more lensesand/or a beam restrictor. As in the solution of FIG. 3, a ‘dark’ zone 5can be designed between the receiver beam 4 and the transmitter beam 3in the solution of FIG. 5, even though such a zone is not shown in FIG.5. The ‘dark’ zone can be implemented, for example, by restricting thebeam sent from the transmitter 1, or by making a non-reflecting area onthe surface of the curved mirror 53 or 54 close to the boundary linebetween the mirrors.

The solution of FIG. 6 includes an integrated optical component 6 and areflecting element 7, with the aid of which a transmitter beam 3 and areceiver beam 4 are formed. As in the embodiment of FIG. 5, even thereflecting element 7 is integrated as a single mechanical piece with theintegrated optical component 6. In this solution, the integrated opticalcomponent 6 consists of a lens 63 and a curved mirror 64, which isattached to the surface of the lens 63. The lens 63 has a focal point,to which the receiver beam 4 is focussed from the edge area of the lens63. The receiver 2 is located at this focal point. The curved mirror 64in turn reflects the focal point outside of the beams 3 and 4. Thetransmitter 1 is located at the focal point reflected by the curvedmirror 64, in such a way that the light obtained from the transmitter 1is reflected from the surface of the curved mirror 64, to form atransmitter beam 3 of the desired shape.

A particularly interesting feature of the embodiment of FIG. 6 is thatit does not require a separate reflecting element 7, as the curvedmirror 64 included in the integrated optical component 6 is itselfreflecting. Thus, the reflecting element 7 too is integrated as a singlemechanical piece with the integrated optical component 6. This has thesignificant effect that the lidar according to such an embodiment alsodoes not require the reflecting element 7 and the integrated opticalcomponent 6 to be focussed separately, instead they are focussed at thesame time and are always mutually in the correct position. Thus, in thebasic solution of FIG. 6, only three optical components need bepositioned relative to each other, i.e. the integrated optical component(which also acts as the reflecting element 7) formed by the lens 63 andthe mirror 64, the transmitter 1, and the receiver 2.

In the solution of FIG. 6, as in the solution of FIG. 3, optionalaccessories can be used. Possible accessories include the pre-optics ofthe transmitter 1 or the receiver 2, which can include one or morelenses and/or a beam restrictor. As in the solution of FIG. 3, a ‘dark’zone 5 can be designed between the receiver beam 4 and the transmitterbeam 3. In the embodiment of FIG. 6, the ‘dark’ zone is implemented byplacing a black-out ring 65 around the curved mirror 64, but the ‘dark’zone can certainly also be implemented by restricting the transmitterbeam with a restrictor placed in front of the transmitter 1, or byrestricting the receiver beam 4 with a restrictor placed in front of thereceiver 2.

The solution of FIG. 7 includes an integrated optical component 6 and areflecting element 7, with the aid of which a transmitter beam 3 and areceiver beam 4 are formed. In this solution, the integrated opticalcomponent 6 consists of a single curved mirror 73 with a focal pointoutside of the parallel beams (the transmitter beam 3 and the receiverbeam 4). A mirror 74, which is located more or less in the centre of thebeam proceeding towards the focal point, acts in turn as the reflectingelement 7. The mirror 74 is positioned relative to the transmitter 1 insuch a way that the mirror 74 reflects to the transmitter 1 the focalpoint formed in the central area of the curved mirror 73. Thus, thelight obtained from the transmitter 1 can be reflected and refractedwith the aid of the mirrors 73 and 74 into a transmitter beam 3 of thedesired shape. On the other hand, the mirror 74 is positioned so that itdoes not obscure the field of vision desired for the receiver 2, butpreferably even restricts the receiver beam to the desired shape bycovering the central area in front of the receiver 2. Thus, the receiver2 is located at the focal point formed by the edge area of the curvedmirror 73.

In the basic solution of the embodiment of FIG. 7, as in the solution ofFIG. 3, there are four optical components that have to be positioned inrelation to each other, i.e. the integrated optical component formed bythe curved mirror 73, and the transmitter 1, the receiver 2, and themirror 74.

In the solution of FIG. 7, as in the solution of FIG. 3, optionalaccessories can be used. Possible accessories include the pre-optics ofthe transmitter 1 or the receiver 2, which can include one or morelenses and/or a beam restrictor. As in the solution of FIG. 3, in thesolution of FIG. 7 too there is a ‘dark’ zone 5 designed between thereceiver beam 4 and the transmitter beam 3.

The solution of FIG. 8 includes an integrated optical component 6 and areflecting element 7, with the aid of which a transmitter beam 3 and areceiver beam 4 are formed. In this solution, the integrated opticalcomponent 6 is formed by a single curved mirror 83, which has a focalpoint outside the parallel beams (the transmitter beam 3 and thereceiver beam 4). A mirror 84, in which there is a hole located more orless in the central zone of the beam proceeding towards the focal point,acts in turn as the reflecting element 7. The transmitter 1 is locatedat the focal point of the curved mirror 83, so that the light obtainedfrom the transmitter 1 travels through the hole in the mirror 84 and isrefracted by the central area of the curved mirror 83 to form atransmitter beam 3 of the desired shape.

The mirror 84, on the other hand, is positioned so that the lightarriving from the edge areas of the curved mirror 83 is reflectedtowards the reflected focal point. The receiver 2 is located at thisreflected focal point.

In the basic solution of the embodiment of FIG. 8, as in the solution ofFIG. 3, there are four optical components that have to be positionedrelative to each other, i.e. the integrated optical component formed bythe curved mirror 83, and the transmitter 1, the receiver 2, and themirror 84.

In the solution of FIG. 8, as in the solution of FIG. 3, optionalaccessories can be used. Possible accessories include, for example, thepre-optics of the transmitter 1 or the receiver 2, which can include oneor more lenses and/or a beam restrictor. As in FIG. 3, in the solutionof FIG. 8 too a ‘dark’ zone 5 can be designed between the receiver beam4 and the transmitter beam 3, even though such a zone is not shown inFIG. 8. The ‘dark’ zone can, for example, be implemented by restrictingthe beam sent by the transmitter 1, or by making a non-reflecting areaon the surface of the curved mirror 83, between the said central areaand the edge area.

Embodiments of the invention, differing from those disclosed above, canalso be contemplated. For example, the embodiments disclosed above canbe modified so that the locations of the transmitter and the receiverare reversed. In such an embodiment, the transmitter beam surrounds thereceiver beam. The embodiments of FIGS. 3, 4, 7, and 8 can also bemodified in such a way that a specific curve is designed in the mirrorsacting as the reflecting element 7, allowing these mirrors to alsoparticipate in refracting light in the optical system of the lidar. Theintention, however, is to implement the principal refraction with theaid of the integrated optical component 6.

In connection with the embodiments of the Figures, it has also beenstated that the transmitter beam is formed by the central area of theintegrated optical component 6. This does not mean, however, that thetransmitter beam 3 must be precisely centred, or that it always evencovers the central area of the integrated optical component 6. Theformation of the transmitter beam 3 can equally well be positioned totake place near the edge of the integrated optical component 6, in whichcase the receiver beam surrounding the transmitter beam 3 will beconsiderably wider on one side of the transmitter beam 3. In fact, it isnot even necessary for the receiver beam 4 (or, in an invertedembodiment, the transmitter beam 3) to completely surround thetransmitter beam 3. From the point of view of the measurement stability,however, it is preferable for the receiver beam 4 to surround thetransmitter beam 3, at least more or less completely. Further, it ispreferable for the transmitter beam 3 to be located more or less in thecentral zone of the receiver beam 4 and for the receiver beam 4 and thetransmitter beam 3 to be shaped rotationally symmetrically.Nevertheless, the receiver beam 4 and the transmitter beam 3 can also bedesigned to be asymmetrical, or to be symmetrical in some other way,without, however, deviating from the scope of the invention.

The invention being thus described, it will be obvious that the same maybe varied in many ways. Such variations are not to be regarded as adeparture from the spirit and scope of the invention, and all suchmodifications as would be obvious to one skilled in the art are intendedto be included within the scope of the following claims.

1. A lidar, which includes a transmitter (1) and a receiver (2), as wellas an optical system, which is arranged to direct at least part of lightemitted by the transmitter (1) to form a transmitter beam (3) proceedingtowards an object and to define the receiver beam (4) to the receiver(2), at least part of the light arriving from the area of which isfocussed on the receiver (2), which optical system is implemented sothat the beams (3, 4) immediately in front of the lidar are locatedsubstantially outside of each other and one of the beams (3, 4) at leastpartially surrounds the other beam (4, 3), and wherein the opticalsystem includes an integrated optical component (6), the integratedoptical component (6) consisting of one lens (33, 43) and having a firstarea for the transmitter beam (3) and a second area for forming thereceiver beam (4), and wherein said first area of the integrated opticalcomponent (6) is adapted to form the transmitter beam (3) such thatrefraction of the transmitter beam (3) takes place with the aid of saidfirst area of the integrated optical component (6), wherein the opticalsystem comprises a mirror in order to provide a reflection, so that thefocal point of the light refracted in the second area of the integratedoptical component lies at a distance to a focal point of the lightrefracted in the first area of the integrated optical component, andwherein the transmitter (1) is located at one of said two focal pointsand the receiver (2) is located at the other of said two focal points.2. The lidar according to claim 1, wherein the mirror is provided with ahole, so that the emitted light travels through the hole between thefocal point and the first area of the integrated optical component (6),and the received light is reflected to a focal point reflected from thesurface of the holed mirror.
 3. The lidar according to claim 1, whereinthe mirror creates a reflected focal point of the integrated opticalcomponent (6), in such a way that the light transmitted from thereflected focal point is reflected to the first area of the integratedoptical component (6), the mirror being positioned in such a way thatthe light received through the second area of the integrated opticalcomponent (6) bypasses the mirror and proceeds to the focal point of theintegrated optical component (6).
 4. The lidar according to claim 1,wherein a field of vision (4) of the receiver is essentially annular andis positioned around the transmitter beam (3).
 5. The lidar according toclaim 1, wherein the refraction of the transmitter beam (3) and thereceiver beam (4) takes place principally with the aid of the integratedoptical component (6).
 6. The lidar according to claim 1, wherein thesaid second area of the integrated optical component (6) surrounds thesaid first area, without intersecting the first area.
 7. The lidaraccording to claim 1, wherein the said second area of the integratedoptical component (6) is located in an edge area of the integratedoptical component (6) and the said first area is located in a centralarea of the integrated optical component (6).
 8. The lidar according toclaim 1, wherein the transmitter beam (3) is located immediately infront of the lidar at a distance from a field of vision (4) of thereceiver, thus forming a ‘dark’ zone (5) between the beams (3, 4). 9.The lidar according to claim 1, wherein the transmitter beam (3) and afield of vision (4) are shaped essentially rotationally symmetricallyrelative to a common central axis.
 10. The lidar according to claim 1,wherein in the measurement zone of the lidar, the transmitter beam (3)is located at least partly within a field of vision (4) of the receiver.11. The lidar according to claim 1, wherein the transmitter is arrangedto produce a nearly monochromatic beam of light, the wavelength of whichis in a range 300-5000 mm.
 12. The lidar according to claim 11, whereinthe transmitter is arranged to produce a nearly monochromatic beam oflight, the wavelength of which is in the range 400-2000 mm.
 13. Thelidar according to claim 1, further comprising at least one restrictor(38) between the receiver (2) and the integrated optical component (6),for restricting the beam of light directed from the optical system tothe receiver (2).
 14. The lidar according to claim 1, further comprisingat least one restrictor (36) between the transmitter (1) and theintegrated optical component (6), for restricting the beam of lightdirected from the transmitter (1) to the optical system.
 15. The lidaraccording to claim 1, wherein the lidar is adapted to makemeteorological measurements, including cloud-ceiling and visibilitymeasurements, and to determine a structure or an altitude of atmosphericboundary layers.